As set by the standards, downlink Multiple Input Multiple Output (MIMO) antennas in a Evolved Universal Terrestrial Radio Access (E-UTRA) communication system are precoded using a defined unitary codebook. The throughput and coverage of data and control channel is significantly improved by closed loop MIMO using preceding. A mobile station can select the rank and precoding vector based on the available number of receive and transmit antennas and the known precoding matrix indexes (PMI). The base station, or Node-B, uses the selected PMI it receives from the mobile station in configuring the weights on the MIMO transmit antennas and transmitting signals to the mobile stations over the shared and signaling channel.
Nonetheless, there is a requirement that the base station signals the relevant mobile stations the PMI that is being used to transmit data using the shared channel and control signaling using the control channel. Even though the mobile station selected a PMI, that PMI may not be the index used by the base station. For example, the base station may have misunderstood the originally selected PMI, or the base station may have data unknown to the mobile station that makes a choice for a different PMI more appropriate than the one originally selected by the mobile station.
A base station can notify the mobile station of the PMI used by the base station and use dedicated reference signal to demodulate the PMI information. This technique of notification increases downlink overhead and increases the system complexity since multiple modes have to be supported. Signaling in the downlink control channel can also be used to notify the mobile station of the PMI used by the base station. This method of notification also increases downlink signaling overhead, also increases the system complexity since multiple formats of control channel have to be supported and the control channel itself cannot be using preceding.
In view of the foregoing, there is a need in which mobile station can detect the PMI used by the base station without additional overhead.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.